Embodiments disclosed herein relate to systems and methods for pigment processing, particularly for toner applications. More particularly, embodiments disclosed herein relate to the use of magnetic actuated milling to facilitate making pigment dispersions.
Pigment dispersions are an important component in the preparation of emulsion aggregation (EA) toner. In order for pigment particles to form aggregates with the latex particles, the pigment particles are ideally smaller or at least comparable in size to the latex particles. Pigments are usually dispersed in a medium and milled until average pigment particle size is in a range from about 100 nm to about 200 nm.
Conventional pigment dispersion processes may be energy intensive and lengthy and the cost associated with their preparation can be as high as 50% of the total pigment dispersion cost. For pigment dispersion utilizing an in-line rotor-stator type homogenizer, the length of process time may exceed four hours. Among CMYK pigments, carbon black is one of the easiest and least expensive pigments to disperse, while colored pigments, such as magenta and yellow pigments, are harder to disperse and hence longer milling times are typically required.
Several types of solenoids or AC motors have been used to provide an alternating magnetic field to drive the movement of magnetic particles for milling. The electromagnetic forces provided by AC solenoids are generally weak, on the order of about 400 Gauss. Additionally, both switching relay and coils tend to heat up in just minutes in such devices rendering longer milling times impractical. While cooling may be possible, relays and coils are often too well insulated to be cooled effectively.
There remains a need to develop a dispersion technology which reduces processing time and cost, without sacrificing benchmark material properties (e.g., small size and relatively narrow particle size distribution).